The invention relates to a power-supply device for an electric motor that can be operated in a normal operating mode and/or in an emergency operating mode, especially for an actuator in a motor vehicle. The invention also relates to a method for the operation of an electric motor in a normal operating mode and/or an emergency operating mode, especially for an actuator in a motor vehicle.
It is known to adjust the position of adjustable components in a motor vehicle by means of an actuator, in order to control systems in the motor vehicle or to influence and/or trigger system states, especially in a targeted way, for example, in a camshaft or camshaft adjuster for a motor vehicle internal combustion engine or a valve or a valve adjuster for fuel injection. Such motor vehicle actuators have the effect, as is further known, of adjusting the components by means of electric motors (servomotors), for example, by means of known three-phase current motors, such as three-phase current synchronous or asynchronous motors.
A three-phase current asynchronous motor, called asynchronous motor for short below, is an electric motor, which is operated with a three-phase current. Viewed electrically, an asynchronous motor is a short-circuited three-phase current transformer, whose secondary winding (a rotor) is mounted so that it can rotate. Through an operating voltage applied to a stator winding, in the interior of the machine a rotating magnetic field is generated, which induces a current in the short-circuited inner winding (armature). This current itself establishes, in turn, a magnetic field around the rotor. Both magnetic fields interact so that only one torque is generated.
A three-phase current synchronous motor, called synchronous motor for short below, is an electric motor, which is also operated with a three-phase current. On the outside it has a winding, which generates a magnetic alternating field. The rotor carries either permanent magnets or an excitement winding for generating a field. In the synchronous motor, the rotor with the excitation lags the alternating field. In contrast to the three-phase current asynchronous motor, the synchronous machine has no slippage, because no voltages have to be induced in the rotor. Therefore, one can rely on a constant rotational speed for operation on a rigid network.
In modern actuators, the electric motors are usually controlled electronically using electronic control devices, wherein operating states (system states) of the system controlled by means of the electric motor to be controlled and/or the actuator to be adjusted are monitored. If the monitored operating states move within certain, given limits, the monitored system operates in a state usually designated as a normal state.
However, if operating states outside of the limits of the normal operating states are determined, which can be designated, for example, as system faults—in short, if system faults are determined—then the control device usually provides a controller for an emergency operation or emergency operating mode, in order to prevent damages to the controlled system.
Such an emergency mode can be, for example, an adjustment of the component adjustable by the actuator into a safe position, also designated as a fail-safe position. For example, here an electronic camshaft adjuster is known for a motor vehicle combustion engine in which, if there is a fault, the electric motor of the actuator is separated by a controller and the electric motor sets the camshaft into the fail-safe position—if possible at a target adjustment speed to be maintained—such that the combustion engine can still be operated at least with emergency operation properties.
The start-up of the fail-safe position or the adjustment into the fail-safe position can be caused, for example, by a restoring spring on the actuator. A disadvantage is that the restoring spring leads to over-dimensioning of the adjustment system. Another disadvantage is that in the normal operation of the electric motor, the spring force must be overcome, which leads to a higher load in normal operation and/or to higher driving costs of the adjustment system.
The start-up of the fail-safe position can be further caused, for example, by a second (electric) motor connected in parallel. However, this is associated with high technical extra requirements and/or considerable extra costs.
The fail-safe position can be further caused, for example, by a short-circuiting of the (electric) motor, which causes braking of the motor. The braking principle is based on an induced counter voltage of the motor and is therefore dependent on the rotational speed. At smaller rotational speeds, there is no longer a braking moment holding the adjustment system in the fail-safe position, if this position is reached at all. Here, applicant reserves the right to divide the safety concepts for achieving fail-safe positions from the present invention and to pursue them within the scope of sub-applications as standalone subject matter.